Amit Langote wrote:
> See if the attached makes it any better.
>
> Now I know we don't have the runtime pruning in yet, but since the
> proposed patch would extend its functionality I have included its
> description in the comment.
Thanks!
I edited it as attached, to 1. avoid mentioning functionality that
doesn't yet exist, and 2. avoid excessive internal detail (we want a
high-level overview here), which from experience gets outdated pretty
quickly.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
commit 28768290d8d9c58e76e2594a14d5b1f8465ba262[m
Author: Alvaro Herrera <alvhe...@alvh.no-ip.org>
AuthorDate: Sat Apr 7 08:44:12 2018 -0300
CommitDate: Sat Apr 7 09:20:58 2018 -0300
Add some documentation to partprune.c
Author: Amit Langote
Discussion:
https://postgr.es/m/CA+HiwqGzq4D6z=8r0ap+xhbtfcq-4ct+t2ekqje9fpm84_j...@mail.gmail.com
diff --git a/src/backend/partitioning/partprune.c
b/src/backend/partitioning/partprune.c
index 959ee1643d..07b8057e3f 100644
--- a/src/backend/partitioning/partprune.c
+++ b/src/backend/partitioning/partprune.c
@@ -1,10 +1,27 @@
/*-------------------------------------------------------------------------
*
* partprune.c
- * Parses clauses attempting to match them up to partition keys of
a
- * given relation and generates a set of "pruning steps", which
can be
- * later "executed" either from the planner or the executor to
determine
- * the minimum set of partitions which match the given clauses.
+ * Support for partition pruning during query planning
+ *
+ * This module implements partition pruning using the information contained in
+ * table's partition descriptor and query clauses.
+ *
+ * During planning, clauses that can be matched to the table's partition key
+ * are turned into a set of "pruning steps", which are then executed to
+ * produce a set of RTIs of partitions whose bounds satisfy the constraints in
+ * the step. Partitions not in the set are said to have been pruned.
+ *
+ * There are two kinds of pruning steps: a "base" pruning step, which contains
+ * information extracted from one or more clauses that are matched to the
+ * (possibly multi-column) partition key, such as the expressions whose values
+ * to match against partition bounds and operator strategy to associate to
+ * each expression. The other kind is a "combine" pruning step, which combines
+ * the outputs of some other steps using the appropriate combination method.
+ * All steps that are constructed are executed in succession such that for any
+ * "combine" step, all of the steps whose output it depends on are executed
+ * first and their ouput preserved.
+ *
+ * See gen_partprune_steps_internal() for more details on step generation.
*
* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
